1. Field of the Invention
The present invention relates to a structure of vehicle seat which prevents a passenger from being slipped and slid forwardly on the seat when a collision or the like occurs. In particular, the invention is directed to a vehicle seat structure of this kind wherein a vertically movable forward slippage preventive element is provided in a seat cushion of the seat.
2. Description of Prior Art
In the case of an abrupt deceleration or stop of a vehicle, a passenger on a seat in the vehicle is naturally caused to displace forwardly due to inertia. Such forward displacement of the passenger is basically prevented by a seat belt which restrains the passenger to the seat. However, in such an emergency case as a collision, stopping of the vehicle can be so abrupt that, in spite of the restraint of the seat belt, the buttocks portion of the passenger will still slip or slide forward on a seat cushion of the seat and sink into the upper elastic portion of the seat cushion, with it being of a high likelihood that the lower portion of the passenger will be damaged or injured. This is what is called “forward buttocks slippage phenomenon”.
Hitherto, various attempts have been made to prevent such forward buttocks slippage phenomenon. For example, a cross rod is fixedly provided in the seat cushion as a forward buttocks slippage preventive means, the cross rod extending transversely of the forward region of the seat cushion to thereby prevent forward slippage of the passenger's buttocks portion on the seat cushion. Namely, in the case of sudden collision, the passenger's buttocks portion, which is being slipped on and sunk into the seat cushion, is quickly contacted with the cross rod and thus prevented against further forward movement, thereby protecting the lower body portion of the passenger.
However, such fixed provision of cross rod in the seat cushion has been found defective in degrading the cushion touch of the seat cushion and giving a hard touch of the cross rod itself to the buttocks portion of the passenger when he or she sits on the seat cushion.
In order to avoid such unpleasant seating touch, a vertically movable forward buttocks slippage preventive element has been proposed. Namely, it has been proposed that the forward buttocks slippage preventive element is movable between a lower inoperative position where it is normally set at a low level in the seat cushion and an upper operative position where it is raised to a level generally corresponding to a forward buttocks slippage locus along which the buttocks portion of passenger is to be slipped forwardly on the seat cushion in the case of collision or other emergency case. With this arrangement, when a sudden collision occurs, tending to cause a passenger to slip forwardly on the seat cushion, the forward buttocks slippage preventive element is quickly rotated upwardly to the upper operative position to receive the passenger's buttocks portion. For example, this sort of seat structure has been known from the Japanese Laid-Open Patent Pub. No. 7-81466 disclosing an air-bag type arrangement which uses an air bag to prevent the forward buttocks slippage, or the Japanese Laid-Open Patent Pub. No. 2002-2345 disclosing a seat-belt type arrangement which causes vertical movement of a forward buttocks slippage element responsive to a movement of seat belt.
According to the former publication No. 7-81466, a great load caused in an emergency case is detected by a sensor system which in turn sends a signal to a drive mechanism and then an air bag is inflated by the inflating mechanism to raise a forward buttocks slippage preventive plate in the seat cushion. But, such provision of sensor system and inflating mechanism result in making the seat structure complicated and increasing costs involved in assembly thereof, which further increases a whole weight of the seat. In addition thereto, once the air bag has been inflated, it is quite difficult to return the inflated air bag into a normal non-inflate state and re-set the same in a normal storage location, thus requiring replacement air bags for re-use.
On the other hand, according to the latter publication No. 2002-2345, a slidable support member provided with a seat belt buckle, on which a seat cushion is mounted, is slidably engaged with a slide rail device and so arranged as to have an interlocked relation with a forward buttocks slippage preventive element provided in the forward regions of seat back. In a collision or the like, the seat belt, by which a passenger is restrained in the seat, is forcibly pulled forwardly under the influence of inertia, which causes forward movement of the slidable support member and seat cushion relative to the slide rail device. Responsive thereto, the forward buttocks slippage preventive element is raised to receive the buttocks portion of the passenger. Further, the forward buttocks slippage preventive element can be returned to a normal non-use position and a whole of the device can be re-used against another emergency case. Thus, this prior art is superior to the foregoing prior art (7-81466) in terms of simplified structure which does not require any sensor and inflating mechanism and recovery or re-use possibility. However, in this Pub. No. 2002-2345, the seat back itself is moved forwardly to prevent the forward buttocks slippage, which means that it is highly possible for a passenger to be moved with the seat toward a steering wheel or a panel disposed forwardly of the passenger and therefore the passenger may collide with those vehicle interior parts and may be damaged or injured thereby. With this undesired case in view, a technical person will contemplate on providing a biasing means for biasingly returning the seat cushion backwardly to a home position in response to a forward inertia in a collision case or the like. Nonetheless, when the seat cushion is be moved forwardly in a collision or 'the like under inertia, the seat is quickly returned under a biasing force of the biasing means to the home position, which will adversely give an abrupt backward counter force to the passenger. If such backward biasing force is extremely great, the returning of seat is so quick that the passenger will be subjected to a secondary great impact in the backward direction, and thus, he or she may be damage or injured by such secondary great impact. Also, the forward sliding movability of seat back in this prior art will reduce the forward inertia, as a result of which, a whole of the seat back will not be moved to a point sufficient enough to raise the forward buttocks slippage preventive element, or, depending on the situation, the forward buttocks slippage preventive element will be quickly returned to a home position under the backward biasing force of the biasing means and will not work to prevent the passenger's buttocks portion against forward slippage on the seat cushion.